In recent years, information recording media performing contactless communication with reading devices and, especially contactless IC cards, have been widely used in various systems such as transit systems, electronic money, employee ID card systems, logistics management, and the like.
Among communication methods employing contactless information recording media, there are the electromagnetic coupling method, electrostatic coupling method, electromagnetic induction method, and radio wave method depending on the communication frequency band. The electromagnetic induction method is used predominately in communication systems employing a contactless card.
Contactless IC cards using the electromagnetic coupling and electrostatic coupling are standardized by ISO/IEC 10536. The signal frequency of 4.9 MHz is used and two loop-shaped antennas or capacitor plates are provided within the contactless IC card.
Contactless IC cards using the electromagnetic induction are standardized by ISO/IEC 14443, 15693 and 18092. The signal frequency of 13.56 MHz is used and a loop-shaped antenna is provided in the contactless IC card.
Contactless IC cards using the radio wave method are standardized by ISO/IEC 18000. The signal frequency of 2.45 MHz is used and a plate-shaped dipole antenna is provided therein.
The contactless IC card communicates with an external terminal through an antenna connected to an IC chip equipped to the card. In order to obtain favorable communication performance, it is necessary to establish antenna shapes suited to the communication frequency and the IC chip.
As a result, the antenna may become a complex shape, and the quality of the antenna is secured by a method such as patterning by etching a conductive material, printing with a conductive ink, and embedding a coated wire. With these methods, it has been necessary to select a metal having a low resistance value and embody the antenna having the complex shape into a card in order to improve the communication characteristics. As a result, it has not been possible to reduce the card cost.
On the other hand, for a close-range type contactless communication system as a system that is inexpensively and simply configured and performs contactless communication of an electrostatic coupling method in a continuous, wide permissible range from low-speed data to high-speed data, a communication system has been offered. This system configures so as to use the electrostatic capacity formed by planar electrodes arranged on the transmitting side and receiving side respectively being made to face each other as a coupler. The transmitting side supplies a direct baseband signal to the electrode on the transmitting side. This system binarily demodulates the transmitted waveform reaching the electrode of the receiving side with a comparator having a hysteresis characteristic (for example, refer to Patent Document 1).
However, since the electromagnetic induction method is predominant in the communication system using a contactless information recording medium, in order to construct a system with the electrostatic coupling method described in Cited Publication 1, it is necessary to use an IC chip compatible with the electrostatic-coupling method and construct a system.
In addition, when an IC card of an electrostatic-coupling method is displaced or rotated relative to the reading device, there has been a problem in that the communication is not stable.
Furthermore, when the IC card of an electrostatic-coupling method and the aforementioned IC cards of an electromagnetic induction method are bent, there has been a problem in that the IC chip tends to be damaged.    Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2009-135632